No trials are published evaluating muscle adaptations using US in response to clinical treatments for low back pain in the older adult population. Increased muscle size and improved muscle symmetry have been reported in younger adults with low back pain who participate in low back stabilization exercises. These exercises use voluntary contractions of the back muscles with prolonged hold times and low loads. Neuromuscular Electrical Stimulation (NMES) is a treatment modality that increases muscle activity when voluntary activity is impaired and increases muscle size. Most studies assessing muscle size and activity in response to NMES have been conducted in the knee muscles (i.e. the quadriceps), while the impact of NMES on the back muscles remains relatively unexplored. Given the potential to evaluate back muscle size and activity with US, this assessment tool may be used to document muscle adaptations to a clinical intervention in older adults with low back pain.